1. Field of the Invention
The present invention relates to a shaft seal structure suitable for application to rotation shafts and the like used in large fluidic machines such as gas turbines, steam turbines, compressors and pumps, and relates also to a turbine that converts fluid thermal energy into rotational energy for generating a motion power, and relates in particular to a shaft seal structure that can be applied to a rotation shaft of the turbine.
2. Description of the Related Art
In general, for gas turbines and steam turbines, a shaft seal structure is provided around the rotation shaft for reducing leakage of combustion gas from the high-pressure-region to the low-pressure-region. An example of such a shaft seal is a leaf seal 1 shown in FIG. 18.
The leaf seal 1 comprises a plurality of layers of planar plates 3, having a predetermined width dimension in the axial direction of the rotation shaft 2, arranged in the circumferential direction of the rotation shaft 2.
The base section of the planar plates 3 of the outer periphery is fixed to a leaf seal ring 5 by means of a brazed section 4, and the tip end of the planar plates 3 is on the inner periphery, and is made to contact the rotation shaft 2 at a given pre-loading value. The tip of each planar plate 3, as shown in FIGS. 18 and 19, slidably contacts the peripheral surface of the rotation shaft 2 at an acute angle with the peripheral surface of the rotation shaft with respect to the rotation direction of the rotation shaft 2 (shown by the arrow d in the diagram).
The planar plate 3 attached to the leaf seal ring 5, as described above, serves as a seal on the outer peripheral surface of the rotation shaft 2, and divides the surrounding space of the rotation shaft 2 into a high pressure region and a low pressure region.
The planar plates 3 of the leaf seal ring 5 are surrounded laterally by a high-pressure-region plate 7 in the high-pressure-region and by a low-pressure-region plate 8 in the low-pressure-region to act as guiding plates to operate in the pressurizing direction.
When the rotation shaft 2 having the leaf seal 1, constructed in the manner described above, is rotated, tip end of each planar plate 3 is floated away from the peripheral surface of the rotation shaft 2 due to the kinematic effect generated by the moving rotation shaft 2, thereby preventing the tips of each strip 3 from contacting the rotation shaft 2. By doing this, wear of the components is prevented.
However, when such a leaf seal 1 is operated at low speeds, such as during the startup, the floating force exerted on each strip 3 is weak. As shown in FIG. 20, the shaft rotates while the tips of the strip 3 are in contact with the peripheral surface of the rotation shaft 2; thus, there is a problem in that friction between the strips 3 and the rotation shaft 2 occurs.
Also, during the highspeed operation of the rotation shaft 2, there is a case in that the extent of thermal expansion of the leaf seal ring 5 and the stator section (not shown) to which the leaf seal ring 5 is attached is greater than that of the rotation shaft 2. In other words, there is a case in that the thermal expansion of the diameter of the leaf seal ring 5 is greater than that of the diameter of the rotation shaft 2, a space 9 is created between the tips of the strips 3 and the rotation shaft 2. As shown in FIG. 21, there is a problem in that the gas leakage increase and the performance of the seal may be lowered.